Laser Science, Quantum Optics Featured at 2004 CLEO/IQEC Conference

Breakthroughs in NASA technologies, medical imaging, and homeland security technology were among the highlights at the 2004 Conference on Lasers and Electro-Optics/International Quantum Electronics Conference (CLEO/IQEC)—a leading conference showcasing new results in laser science, quantum optics, and related fields—which took place May 16-21 in San Francisco, California. The meeting was jointly sponsored by the APS, the Optical Society of America, and the Institute of Electrical and Electronic Engineers/Lasers and Electro-Optics Society.

The featured plenary session explored the history of the maser and future applications for technology; presentations on optics and photonics in bioscience; and optical metrology. There was also a joint symposium celebrating the 50th anniversary of the invention of the maser.

SEEING THE BREATH OF DISEASE. Equipped with the latest advances in optics, researchers are setting their sights on carbonyl sulfide (COS), a molecule that has importance in both the atmosphere and in medicine. Currently, diagnosing lung-transplant rejection requires a biopsy. A non-invasive breath diagnosis would be very desirable, but detecting the typically parts-per-billion levels of the molecule in patients is very challenging. Gerard Wysocki and his colleagues at Rice University have built a new detection system that can detect the COS molecule at very low levels.

The centerpiece of the system is a quantum cascade laser, a device that generates laser light in a part of the spectrum known as the mid-infrared. COS molecules absorb light in a unique part of the mid-infrared spectrum and thereby can reveal their molecular "fingerprint." In the setup, a patient first exhales some breath into a small gas cell. Then, the cascade laser shines precisely tuned infrared light through the cell. COS molecules absorb light in the exact part of the spectrum where the laser is tuned. The detection system records the amount of absorption, and this determines the concentration of the molecules in the breath. The researchers have performed some preliminary tests of the system in human breath samples. Having demonstrated a sensitivity of a part per billion, they are hoping to build a prototype medical device with their technology. Such a system would be reasonably priced for a hospital, at about $30,000.

CATCHING DEFECTS IN SPACE SHUTTLE FOAM. Investigators believe the Space Shuttle Columbia disaster resulted from loosened fuel-tank insulation foam hitting a shuttle wing at high speeds. However, it has been difficult to inspect shuttle foam without damaging it or the fuel tank that it protects. X.-C. Zhang of Rensselaer Polytechnic Institute and his colleagues, in collaboration with scientists from NASA Langley Research Center and Lockheed Martin Space Systems, have used terahertz radiation—a form of light in the far infrared part of the spectrum—to detect small defects in samples of space shuttle foam. If shuttle launches are to continue, this technique could help NASA examine the insulating foam prior to shuttle liftoffs.

In their experiment, the researchers tested four foam samples. They looked for two types of foam defects: air bubbles (called "voids") and de-lams, which are separations between layers of foam or between a layer of foam and the aluminum fuel-tank base. Scanning the foam with terahertz waves, the researchers could catch both types of defects. Recently, NASA has announced that terahertz imaging has been selected as one of two technologies for inspecting the insulation foam for any future shuttle launches.

INVESTIGATING MERCURY'S SURFACE AND INTERIOR. How will scientists measure the topography of Mercury? Developers of the Mercury Laser Altimeter answer this question as the spacecraft is readied for launch in August 2004. Once the spacecraft begins orbiting this hot and dense planet, the laser altimeter will transmit laser pulses towards the planet's surface and four large cones will collect the photons reflected off Mercury's surface. The topography of the planet is determined from the laser pulse time-of- flight and the spacecraft orbit position data. The innovative 4-cone receiver optics design helps maintain focus under large and rapid temperature change as the spacecraft travels from the dark and cold side of Mercury to the sunny and hot side.

Understanding Mercury, one of the most extreme rocky planets, will help us understand Earth's topography, development, magnetic field and interaction with the sun.

REAL-TIME IMAGING OF HUMAN SKIN WITH TINY 2-D SCANNER. A team of researchers from the University of California, Los Angeles, and the Massachusetts Institute of Technology, has built a tiny endoscopic scanner, only 5.5 millimeters across.The scanner combines a 2-D scanning mirror, measuring only 1 millimeter in diameter, with optical coherence tomography. With a resolution of 5 micrometers, this endoscope can scan living tissues and provide real time 3-D images.

Tests at MIT were able to scan live human skin in real-time, capturing up to 20 frames per second, with 5-micrometer axial image resolution. The scanner has a very high resonant frequency and can scan areas quickly.

Konstantin Vodopyanov of Stanford and his colleagues have built a new nonlinear-optics device, based on gallium arsenide (GaAs), capable of producing high-power light for numerous applications including many items on the homeland security wish list. Light that enters the material can be efficiently converted into a wide range of different colors (wavelengths). However, to achieve these effects, researchers have to construct specially tailored crystal structures of GaAs. By combining two layer-by-layer crystal growth techniques known as molecular beam epitaxy and hydride vapor phase epitaxy, the researchers have built the first GaAs structure that operates as an optical parametric oscillator (OPO).

OPOs convert single-color laser light into any of a very wide range of new wavelengths. The new device can produce wavelengths in the entire "fingerprint" region of common molecules (2-17 microns). This is crucial for detecting a wide variety of drugs and explosives.

A GaAs OPO can generate powerful infrared light that aircraft can potentially employ to divert heat-seeking missiles. Moreover, the GaAs OPO can potentially generate the far-infrared light suitable for terahertz imaging at airport security as well as trace gas detection. Another benefit is that GaAs devices are likely to be reasonably priced, as the material has been widely studied. However, fabrication techniques, such as hydride vapor phase epitaxy, need to be developed futher to help bring many of these applications to real world use.

—Compiled by Philip Schewe and Ben Stein, American Institute of Physics

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